Former Massachusetts Sen. Scott P. Brown has been touring New Hampshire relentlessly since announcing earlier this month he is moving toward a challenge to Democratic Sen. Jeanne Shaheen — and his operation is now beginning to take shape.

A Republican source close to Brown said he will likely begin announcing full-time staff for his exploratory committee next week, with Andy Leach remaining senior adviser. A team of allies has helped Brown get a campaign off the ground, including Eric Fehrnstrom, a former Brown and Mitt Romney adviser who toured with Brown over the weekend.

Less than two weeks since entering the race, Brown is still ingratiating himself with the state he's lived in since December. He's fighting to prove his Granite State bonafides with an electorate largely aware of his representation of the Bay State in the Senate.

"Do I have the best credentials? Probably not. 'Cause, you know, whatever. But I have long and strong ties to this state," Brown told AP reporter Steve Peoples.

Shaheen, who hired spokesman Harrell Kirstein last week from the state Democratic Party, launched her first ad of the cycle Monday morning — a statewide radio ad slamming Brown for declining to join the incumbent in an effort to keep outside groups from advertising on the race. As the incumbent began that push last week, Crossroads GPS launched its first TV ad of the 2014 cycle against her.

Brown signed an identical outside-spending pledge with now-Sen. Elizabeth Warren, D-Mass., during their 2012 race, which featured the most candidate spending of any Senate race that cycle.

The promise of an expensive campaign led to fundraising appeals last week on Shaheen's behalf by fellow senators Warren and Dianne Feinstein, D-Calif. Beyond the new radio ad, the Shaheen campaign has pushed to keep the outside-spending pledge on the front burner, including in an op-ed from the senator and memo from campaign manager Mike Vlacich. Shaheen also pushed the issue during at least one of her stops in the state last week during the Senate recess.

The sudden commotion reflects the New England state's new position within the midterm election cycle's competitive playing field. While Shaheen remains favored (Rothenberg Political Report/Roll Call rates the race Democratic Favored ,) Brown's candidacy alone expanded the number of Democratic seats in play, as the GOP aims for a net gain of at least six seats to win the majority .